Lecture 23: Peripheral Nervous System (PNS)

Vocabulary practice flashcards covering divisions of the PNS, sensory receptor types, sensory processing, nerve anatomy, nerve regeneration, and all 12 cranial nerves.

Peripheral Nervous System (PNS)

Nervous structures outside the brain and spinal cord that connect the body with the central nervous system (CNS).

Sensory (afferent) pathways

Pathways that bring input to the central nervous system (Afferent Arrives).

Motor (efferent) pathways

Pathways that carry output from the central nervous system (Efferent Exits).

Somatic nervous system

Motor pathway division of the PNS responsible for skeletal muscle control.

Autonomic nervous system

Motor pathway division of the PNS responsible for involuntary control, subdivided into sympathetic and parasympathetic divisions.

Mechanoreceptors

Sensory receptors that detect touch, pressure, vibration, and stretch.

Thermoreceptors

Sensory receptors that detect temperature.

Photoreceptors

Sensory receptors that detect light.

Chemoreceptors

Sensory receptors that detect chemicals, including taste, smell, and blood chemistry.

Nociceptors

Sensory receptors that detect potentially damaging or painful stimuli.

Exteroceptors

Sensory receptors classified by location that detect stimuli coming from outside the body (skin).

Interoceptors

Sensory receptors classified by location that monitor stimuli from internal organs and vessels.

Proprioceptors

Sensory receptors located in muscles, tendons, and joints that detect body position and movement.

Free / nonencapsulated nerve endings

Receptors lacking a connective tissue capsule that respond to pain, temperature, and itch; includes free nerve endings, Merkel discs, and hair follicle receptors.

Encapsulated nerve endings

Receptors enclosed within a connective tissue capsule that detect specialized touch, pressure, vibration, and stretch; includes Meissner, Pacinian, and Ruffini corpuscles.

Meissner corpuscles

Encapsulated nerve endings that respond to light touch and low-frequency vibration.

Pacinian corpuscles

Encapsulated nerve endings that respond to deep pressure and high-frequency vibration.

Ruffini corpuscles

Encapsulated nerve endings that detect deep pressure and stretch.

Muscle spindle

Encapsulated receptor that detects muscle stretch.

Tendon organ

Encapsulated receptor that detects tension in tendons.

Sensation

The awareness of a stimulus.

Perception

The conscious interpretation of a stimulus.

Transduction

The process at the receptor level that converts stimulus energy into a graded potential.

Phasic receptors

Fast-adapting receptors that give a brief response, especially to changes in stimuli (e.g., Pacinian and Meissner corpuscles).

Tonic receptors

Slow-adapting or non-adapting receptors that maintain a continued response while a stimulus remains (e.g., nociceptors and proprioceptors).

Endoneurium

Connective tissue sheath that surrounds each individual axon and its associated Schwann cell.

Perineurium

Connective tissue layer that surrounds a fascicle (a bundle of axons).

Epineurium

Tough, outermost connective tissue sheath that surrounds the entire nerve.

Ganglia

Clusters of neuron cell bodies in the PNS; dorsal root ganglia are sensory and autonomic ganglia are motor.

PNS axon regrowth rate

The speed at which a regenerating PNS axon typically regrows, which is approximately $1.5\,\text{mm/day}$.

Olfactory nerve (CN I)

Sensory cranial nerve responsible for smell.

Optic nerve (CN II)

Sensory cranial nerve responsible for vision.

Oculomotor nerve (CN III)

Motor cranial nerve responsible for eye movement, eyelid movement, and pupil constriction.

Trochlear nerve (CN IV)

Motor cranial nerve responsible for eye movement.

Trigeminal nerve (CN V)

Mixed cranial nerve responsible for facial sensation and chewing.

Abducens nerve (CN VI)

Motor cranial nerve responsible for moving the eye outward.

Facial nerve (CN VII)

Mixed cranial nerve responsible for facial expression, taste, and the secretion of tears and saliva.

Vestibulocochlear nerve (CN VIII)

Sensory cranial nerve responsible for hearing and balance.

Glossopharyngeal nerve (CN IX)

Mixed cranial nerve responsible for swallowing, taste, and salivation.

Vagus nerve (CN X)

Mixed cranial nerve responsible for regulating autonomic functions of the heart, lungs, and digestion.

Accessory nerve (CN XI)

Motor cranial nerve responsible for head rotation and shoulder shrug.

Hypoglossal nerve (CN XII)

Motor cranial nerve responsible for tongue movement.